пятница, 11 февраля 2011 г.

Guitar electronics

Because the sound produced by the strings of a solid-bodyelectric guitar is very low, pickups are mounted; all pickups rely on the same principle: the movement of the strings - which have to be made of some kind of material that is conducive to magnetization (like nickel) - has an effect on a magnetic field created by one or several permanent magnets. Inside thin enameled copper wire, which is wound around these magnets or around material magnetized by bar magnets, an electric current proportional tothe strings' vibrations is generated. Via a cord this alternatingcurrent is then directed into an amplifier and made audiblethrough a speaker.

A single-coil (shown at right) is a pickup that usually produces a
bright, clear sound. There are however, some types with a much
darker sound, like for instance the P-90 (shown on page 44). A
single-coil has four or six permanent magnets wound with 7,000
to 10,000 windings of 0.06mm-thin copper wire. Such pickups
are very popular on account of their sound, but they unfortunately
also have one disadvantage: in a world where we are constantly
surrounded by a great number of electromagnetic fields
an interference signal is generated in the pickup as soon as it gets
anywhere near a mains socket, a light bulb or a fluorescent light,
and an interfering hum equal in pitch to the mains frequency is
superimposed on the guitar signal.

The humbucker - because of the way it is built - is unaffected by
interference. It has two identical coils wired out-of-phase in a
series connection, each with a different pole of the magnet
facing the strings. Any interfering hum passed on via the air is
now picked up by both coils, with the result of one coil cancelling
the hum of the other. In order to prevent the same mutual
cancellation of the current magnetically induced by the vibrating
strings, the magnets in the two coils are placed in opposite
directions, so that the top end of one coil is magnetically south
and the top end of the other coil magnetically north. This has the
additional advantage of the two currents adding up instead of
cancelling each other out and the pickup producing a signal
twice as strong as that of a single-coil pickup. A humbucker
sounds “darker”, bassier, more “middly” than a single-coil pickup
because due to the distance between the magnetic poles of the
two coils the strings induce two differing signals, leading to the
cancellation of certain higher frequencies.